Controlling Network Access

Computers are often part of a network of computers. A network allows connected
computers to exchange information. Networked computers can access data and other resources from
other computers on the network. Computer networks create a powerful and sophisticated computing
environment. However, networks complicate computer security.

For example, within a network of computers, individual systems allow the sharing of
information. Unauthorized access is a security risk. Because many people have access to
a network, unauthorized access is more likely, especially through user error. A poor
use of passwords can also allow unauthorized access.

Network Security Mechanisms

Network security is usually based on limiting or blocking operations from remote systems.
The following figure describes the security restrictions that you can impose on remote
operations.

Figure 2-1 Security Restrictions for Remote Operations

Authentication and Authorization for Remote Access

Authentication is a way to restrict access to specific users when these users
access a remote system. Authentication can be set up at both the system
level and the network level. After a user has gained access to a
remote system, authorization is a way to restrict operations that the user can
perform. The following table lists the services that provide authentication and authorization.

The remote login commands enable users to log in to a
remote system over the network and use its resources. Some of the remote
login commands are rlogin, rcp, and ftp. If you are a “trusted host,” authentication
is automatic. Otherwise, you are asked to authenticate yourself.

The Simple Authentication and Security
Layer (SASL) is a framework that provides authentication and optional security services to
network protocols. Plugins enable you to choose an appropriate authentication protocol.

Secure RPC can also be used to provide additional security
in an NFS environment. An NFS environment with secure RPC is called Secure
NFS. Secure NFS uses Diffie-Hellman authentication for public keys.

Secure Shell encrypts network
traffic over an unsecured network. Secure Shell provides authentication by the use of
passwords, public keys, or both. Secure Shell uses RSA and DSA authentication for
public keys.

A possible substitute for Secure RPC is the Oracle Solaris privileged port mechanism. A
privileged port is assigned a port number less than 1024. After a client system
has authenticated the client's credential, the client builds a connection to the server
by using the privileged port. The server then verifies the client credential by
examining the connection's port number.

Clients that are not running Oracle Solaris software might be unable to
communicate by using the privileged port. If the clients cannot communicate over the
port, you see an error message that appears similar to the following:

“Weak Authentication
NFS request from unprivileged port”

Firewall Systems

You can set up a firewall system to protect the resources in
your network from outside access. A firewall system is a secure host that acts as
a barrier between your internal network and outside networks. The internal network treats
every other network as untrusted. You should consider this setup as mandatory between
your internal network and any external networks, such as the Internet, with which
you communicate.

A firewall acts as a gateway and as a barrier. A firewall
acts as a gateway that passes data between the networks. A firewall acts
as a barrier that blocks the free passage of data to and from
the network. The firewall requires a user on the internal network to log
in to the firewall system to access hosts on remote networks. Similarly, a
user on an outside network must first log in to the firewall system
before being granted access to a host on the internal network.

A firewall can also be useful between some internal networks. For example, you
can set up a firewall or a secure gateway computer to restrict the
transfer of packets. The gateway can forbid packet exchange between two networks, unless
the gateway computer is the source address or the destination address of the
packet. A firewall should also be set up to forward packets for particular
protocols only. For example, you can allow packets for transferring mail, but not
allow packets for the telnet or the rlogin command. ASET, when run
at high security, disables the forwarding of Internet Protocol (IP) packets.

In addition, all electronic mail that is sent from the internal network is
first sent to the firewall system. The firewall then transfers the mail to
a host on an external network. The firewall system also receives all
incoming electronic mail, and distributes the mail to the hosts on the internal
network.

Caution - A firewall prevents unauthorized users from accessing the hosts on your network. You
should maintain strict and rigidly enforced security on the firewall, but security on
other hosts on the network can be more relaxed. However, an intruder who
can break into your firewall system can then gain access to all the
other hosts on the internal network.

A firewall system should not have any trusted hosts. A trusted host is a
host from which a user can log in without being required to supply
a password. A firewall system should not share any of its file systems,
or mount any file systems from other servers.

The following technologies can be used to harden a system into a
firewall:

The Oracle Solaris Security Toolkit, informally known as the JASS toolkit, can harden an Oracle Solaris system into a firewall. The toolkit can be downloaded from the Sun Downloads web site at Oracle Sun.

Encryption and Firewall Systems

Most local area networks transmit data between computers in blocks that are called
packets. Through a procedure that is called packet smashing, unauthorized users from outside
the network can corrupt or destroy data.

Packet smashing involves capturing the packets before the packets reach their destination. The
intruder then injects arbitrary data into the contents, and sends the packets back
on their original course. On a local area network, packet smashing is impossible
because packets reach all systems, including the server, at the same time. Packet
smashing is possible on a gateway, however, so make sure that all gateways
on the network are protected.

The most dangerous attacks affect the integrity of the data. Such attacks involve
changing the contents of the packets or impersonating a user. Attacks that involve
eavesdropping do not compromise data integrity. An eavesdropper records conversations for later replay.
An eavesdropper does not impersonate a user. Although eavesdropping attacks do not attack
data integrity, the attacks do affect privacy. You can protect the privacy of
sensitive information by encrypting data that goes over the network.